Many types of objects are manufactured using rotary-tool milling and other types of subtractive manufacturing processes. Typically, a single object is made from a single body of material, or “workpiece,” such as a block or slab of steel or aluminum. For example, steel and aluminum parts for any of a wide variety of assemblies are often machined from individual workpieces using one or more milling machines. However, making such machined parts can be labor intensive as operators load and unload individual workpieces to and from milling machines.